1) Field of the Invention
The present invention relates to an axial multi-piston compressor comprising a drive shaft, a cylinder block having cylinder bores formed therein and surrounding the drive shaft, and a plurality of pistons slidably received in the cylinder bores, respectively, wherein the pistons are successively reciprocated in the cylinder bores by a rotation of the drive shaft so that a suction stroke and a discharge stroke are alternately executed in each of the cylinder bores.
2) Description of the Related Art
Japanese Unexamined Patent Publication (Kokai) No. 59(1984)-145378 discloses a swash plate type compressor as representative of an axial multi-piston compressor, which may be incorporated in an air-conditioning system used in a vehicle such as an automobile. This swash plate type compressor comprises: front and rear cylinder blocks axially combined to form a swash plate chamber therebetween, the combined cylinder blocks having a same number of cylinder bores radially formed therein and arranged with respect to the central axis thereof, the cylinder bores of the front cylinder block being aligned and registered with the cylinder bores of the rear cylinder block, respectively, with the swash plate chamber intervening therebetween; double-headed pistons slidably received in the pairs of aligned cylinder bores, respectively; front and rear housings fixed to front and rear end faces of the combined cylinder blocks through the intermediary of front and rear valve plate assemblies, respectively, the front and rear housings each forming a suction chamber and a discharge chamber together with the corresponding one of the front and rear valve plate assemblies; a rotatable drive shaft arranged so as to be axially extended through the front housing and the combined cylinder blocks and a swash plate securely mounted on the drive shaft within the swash plate chamber and engaging with the double-headed pistons to cause these pistons to be reciprocated in the pairs of aligned cylinder bores, respectively, by the rotation of the swash plate.
The front and rear valve plate assemblies in particular have substantially the same construction, in that each comprises: a disc-like member having sets of a suction port and a discharge port each set being able to communicate with the corresponding one of the cylinder bores of the front or rear cylinder block; an inner valve sheet attached to the inner side surface of the disc-like member and having suction reed valve elements formed integrally therein, each of which is arranged so as to open and close the corresponding suction port of the disc-like member; and an outer valve sheet attached to the outer side surface of the disc-like member and having discharge reed valve elements formed integrally therein, each of which is arranged so as to open and close the corresponding discharge port of the disc-like member. Each of the front and rear valve plate assemblies is also provided with suction openings aligned with passages formed in the front or rear cylinder block, respectively, whereby the suction chambers formed by the front and rear housings are in communication with the swash plate chamber into which a fluid or refrigerant is introduced from an evaporator of an air-conditioning system, through a suitable inlet port formed in the combined cylinder blocks.
In the swash plate type compressor as mentioned above, the drive shaft is driven by the engine of a vehicle, such as an automobile, so that the swash plate is rotated within the swash plate chamber, and the rotational movement of the swash plate causes the double-headed pistons to be reciprocated in the pairs of aligned cylinder bores. When each piston is reciprocated in the aligned cylinder bores, a suction stroke is executed in one of the aligned cylinder bores and a compression stroke is executed in the other cylinder bore. During the suction stroke, the suction reed valve element is opened and the discharge reed valve element is closed, whereby the refrigerant is delivered from the suction chamber to the cylinder bore through the suction port. During the compression stroke, the suction reed valve element concerned is closed and the discharge reed valve element concerned is opened, whereby the delivered refrigerant is compressed and discharged from the cylinder bore into the discharge chamber, through the discharge reed valve element.
When the compression stroke is finished, i.e., when the piston reaches top dead center, a small part of the compressed refrigerant is inevitably left in a fine space defined between the piston head and the valve plate assembly and in the discharge port formed in the valve plate assembly. Accordingly, when the piston is initially moved from the top dead center position toward bottom dead center, i.e., when the suction stroke is initiated, the refrigerant cannot be immediately introduced from the suction chamber into the cylinder bore through the suction reed valve element, because the residual part of the compressed refrigerant has a higher pressure than that of suction chamber. Namely, at the beginning of the suction stroke, the residual part of the compressed refrigerant is merely expanded in the cylinder bore, and thus the introduction of the refrigerant from the suction chamber into the cylinder bore cannot take place until the pressure of the residual part of the compressed refrigerant becomes lower than that of the suction chamber.
Therefore, in the conventional axial multi-piston compressor as mentioned above, a practical suction volume of the refrigerant, which can be obtained during the suction stroke, is lower than a theoretical suction volume thereof due to the residual part of the compressed refrigerant, and thus it is impossible to sufficiently realize out a theoretical performance from the conventional axial multi-piston compressor.